1. Field of the Invention
This invention relates to a multiple display control apparatus for a television receiver, which switches a plurality of television signals used therein and displays them on a display tube.
2. Description of the Prior Art
The television receiver, in some cases, switches a plurality of signals to be displayed on a display tube, which will be described herein as to two kinds of signals for better understanding as follows:
Referring to FIG. 1, a block diagram of the conventional example is shown, in which the output of a videochroma circuit in the television receiver is assumed to be of three primary colors of R (red), G (green) and B (blue).
Referring to FIG. 1, reference numeral 1 designates a first television signal input terminal, 2 designates a second television signal input terminal, 3 designates a signal process circuit, 4R designates a first R-signal output, 5R designates a second R-signal output, 6R designates a R-signal switching circuit, 4G designates a first G-signal output, 5G designates a second G-signal output, 6G designates a G-signal switching circuit, 4B designates a first B-signal output, 5B designates a second signal output, 6B designates a B-signal switching circuit, 7 designates a control signal generator means, 8 designates a television signal output, 9 designates a first control signal output, 10 designates a switch signal output, 11R designates a R-output terminal, 11G designates a G-signal output terminal, and 11B designates a B-signal output terminal. The R-signal switching circuit 6R, G-signal switching circuit 6G and B-signal switching circuit 6B, are quite the same in function so that the R-signal, G-signal and B-signal are not distinguished from each other in use. In a case where the signal process circuit 3 functions not for the three primary colors of red, green and blue, but for the color difference signal (R-Y, G-Y, B-Y) and luminance signal (Y), further one system of switching circuit need only be added, which is the same as the three primary colors red, green and blue.
In FIG. 1, a video signal is given to the first television signal input terminal 1 and processed at the signal process circuit 3 to thereby obtain the three primary colors of red, green and blue in the first signal output 4. The second television signal input terminal 2 is given other video signals or a video signal the same as that given to the first television signal input terminal 1, the other video signals being processed by the signal process circuit 3 so that the three primary colors of red, green and blue are obtained in the second signal output 5. The video signal the same as that given to the first television signal input terminal 1 is used when other information (for example, in the case of teletext) is superposed on one television signal. In this case, the signal process circuit 3 retrieves the character or pattern signal and decodes it to thereby obtain the three primary colors of red, green and blue in the second signal output 5.
On the other hand, the television signal output 8 outputs a first or second television signal, by which a control signal is generated at the control signal generator means 7. The control signal generated therein is obtained as an output signal at the control signal output 9 and switch signal output 10. According to the switch signal outputted from the switch signal output 10, the first and second television signals are switched by the switching circuits 6 and outputted to the output terminals 11.
The circuit of conventional example in FIG. 1, however, has been defective in that the picture becomes very indistinct when the first signal output 4 is about equal in the brightness level or in the chroma level to the second signal output 5.